1. Field of the Invention
The present invention relates to solder stops. More specifically, the present invention relates to solder stops on electrical contacts and to methods of making electrical contacts having solder stops.
2. Description of the Related Art
As shown in FIG. 6, it is well known in the art to use solder 64 to form an electrical connection between a connection pad 65 on a printed circuit board 66 and the contact tail 63 of an electrical contact 60. When the solder 64 is reflowed to join the contact tail 63 of the electrical contact 60 to the connection pad 65 on the printed circuit board 66, the solder 64 will wick up the length of the contact body 61, which reduces the amount of solder 64 located between the contact tail 63 of the electrical contact 60 and connection pad 65 on the printed circuit board 66.
The reduction in the amount of solder has the following disadvantageous effects: (a) causes a reduction in the electrical performance of the electrical connection between the electrical contact and the printed circuit board; (b) causes a reduction in the integrity of the mechanical connection between the electrical contact and the printed circuit board; (c) hinders mating of the electrical contact with the printed circuit board; and (d) reduces the aesthetics of the completed mechanical connection.
Several techniques are known in the art to prevent solder wicking, and more specifically, to prevent solder from wicking up along the length of the contact body of an electrical connector. First, it is known to use a nickel barrier to prevent solder wicking. Nickel is known as a solder anti-wicking material. A typical electrical contact is formed by coating or plating a base layer of copper or copper alloy with a nickel layer. The nickel layer is then coated or plated with an additional layer of tin, gold, or silver.
In order to use the nickel layer as an anti-wicking layer, selective plating, belt masking, spot plating, and controlled depth plating are typically required. In selective plating, the additional layer must be selectively plated such that a portion of the nickel layer is left exposed. This is accomplished by using removable mask materials such that a portion of the nickel layer is covered when the additional layer is plated. After the additional layer is plated, the removable mask materials are removed, along with the additional layer, such that the nickel layer is exposed.
In belt masking, the contact is pinched between two belts. Then, the portion of the contact that is not pinched between the belts is plated.
In spot plating, the contact is pinched between two specialized belts. Specialized belts used in spot plating are different than the belts used in belt masking because they have an opening in which a plating solution is sprayed through. Thus, only the region of the contact exposed by the opening of the specialized belt is plated.
In controlled depth plating, the contact is suspended at a given height with the contact partially submerged in a plating bath. The contact is plated only where the contact is submerged in the plating bath.
A problem with these techniques is that it is hard to accurately plate the additional layer such that nickel layer is exposed in a location that is most effective for preventing the wicking of the solder. This problem increases the cost of production of any contact that uses the above-described techniques. An additional problem with these techniques is that exposed nickel is not a very effective anti-wicking material.
It is known that the anti-wicking characteristic of nickel is improved by oxidizing the nickel. However, the flux used to facilitate soldering acts as an activating agent that helps to remove impurities and re-activates the surface. Thus, the flux reduces the effectiveness of the oxidized nickel as an anti-wicking material.
It is also known to use a post-plating punch to prevent solder wicking. After the contact is plated, a hole is punched into the contact such that the base layer of copper or copper alloy is exposed. The hole with the exposed base layer physically prevents solder from wicking up the contact around the hole. This is a mechanical solution as opposed to a chemical solution to the solder wicking problem.
A problem with this technique is that the hole in the contact acts to degrade any electrical signal traveling through the contact and to degrade the mechanical strength of the contact. Another problem with this technique is the cost of the secondary process of punching a hole during manufacturing of the contact.
Further, it is also known to use selective plating using an ink mask to prevent solder wicking. Before the contact is plated, an ink is printed onto the base layer of copper or copper alloy. The contact is then plated with metal. Any metal used during the plating will not adhere to the ink. After the plating is completed, the ink is removed to expose the copper or copper alloy, and thus, the ink is not a permanent part of the contact, but instead is only temporarily used during the contact manufacturing process. Thus, the contact has a portion in which the base layer of copper or copper alloy is exposed and oxidized. Solder is prevented from wicking because of the oxidization of the copper or copper alloy.
A problem with this technique is that it is very costly because of the materials and processes used.
In addition, it is known to use a post assembly applied solder mask to prevent solder wicking. That is, after the contact has been assembled, a solder mask, for example, Kapton Tape or fluorine coating, is applied to the contact to prevent wicking.
Some problems with this technique are the cost associated with the additional assembly step and the cost of the solder mask. Another problem with this technique is that not all electrical connectors are arranged such that enough space is available to add the tape.
It is also known to use molded plastic disposed around the contact to prevent solder wicking. A plastic dam is molded around the contact such that a physical barrier is created around the circumference of the contact to prevent the solder from passing.
A problem with this technique is that an additional assembly step is required, which increases the time and labor costs for producing a contact. Another problem with this technique is that it will add extra height to the electrical connector, which will make it unsuitable in situations were an electrical connector having a low profile is needed.
It is further known to press fit the tail of a contact into plastic having a cross-section similar to the cross-section of the contact to prevent solder wicking. The tail of the contact is pressed into an opening in the plastic such that friction keeps the contact in place.
A problem with this technique is that an effective anti-wicking barrier is not created because the opening into which the tail is pressed does not conform precisely to the circumference of the contact. Another problem with this technique is that it is difficult to apply this technique to SMT (Surface Mount Technology) connectors because there is not sufficient space to add the plastic.
Other problems with the above techniques are that excessive materials can inadvertently be used and that the materials can be inadvertently removed during post reflow cleaning. Further, these materials may interfere with the formation of a solder joint.